1. Field of the Invention
The present invention relates to a buffer device for the spiral housing of water turbines and like machines.
2. History of the Related Art
The spiral housings and exhausters of water turbines, turbines, pumps or one- or multi-stage pumps are subjected to an axial thrust due to the action of the pressure on the inlet section of the conduits in such housings. These axial thrusts are known in practice under the term "bottom effect". Effects of thermal origin may also partially appear due to the variation in the water temperature; these effects cause extensions or retractions of the conduit, provoking an additional force on the housings. The seals associated with the housing may be considerably stressed by such forces, which may lead to displacements of the axis of the housings which movement is incompatible with correct operation of the hydroelectric generators.
To solve this problem, various devices are used at the present time:
(1) buffer devices placed in the axis of the inlet conduit and which form distance piece between the housing and a support. These systems allow a displacement of the housing proportional to the rigidity of the support;
(2) sliding joints which avoid transmitting to the machine the effects of thermal origin. With such systems, the bottom effect which is equal to the hydrostatic thrust provokes a moment of pivoting of the housing on its anchorings.
(3) expansion sleeves placed on the conduit and which, thanks to compensations of efforts by application of the pressure of the water of the housing on a surface of appropriate dimensions, efficiently oppose the bottom effect. They further present a sliding joint which enables the efforts to thermal origin to be absorbed.
At first sight, the expansion sleeves are therefore capable of satisfactorily solving the problem of the bottom effects. However, they present several drawbacks:
a. the water serving for counter-pressure in the expansion sleeve is directly that of the conduit, which may lead to fouling at the level of the tappings between the conduit and the seals;
b. dismantling is not possible without emptying the water inlet conduit since no guard member is disposed upstream of the seals;
c. the expansion sleeves are of large dimensions, since, taking into account the thickness of the conduit, in order to cancel the bottom effect proportional to the surface of the conduit, the same pressure of the housing must be applied on an equivalent annular surface.
Thus, if r is the radius of the conduit and R the radius of the expansion sleeve, the surface of this latter, viz. .tau. (R.sup.2 -r.sup.2), must be equal to the surface of the conduit, viz. .tau. r.sup.2, which leads to the following equalities: ##EQU1##
This demonstrates that the outer radius of the expansion sleeve is 1.414 times larger than that of the conduit. To this must also be added the thickness of the housing and of the frame which are appreciable for high pressures.
(d) Three seals are necessary, as is well known in the art and in particular by the ESCHER WYSS Bulletin, Vol. 38, No. 1 of 1965.